Magnetoresistive effect element, magnetic head, sensor, high-frequency filter, and oscillator

ABSTRACT

A nonmagnetic spacer layer in a magnetoresistive effect element includes a nonmagnetic metal layer that is formed of Ag and at least one of a first insertion layer that is disposed on a bottom surface of the nonmagnetic metal layer and a second insertion layer that is disposed on a top surface of the nonmagnetic metal layer. The first insertion layer and the second insertion layer include an Fe alloy that is expressed by Fe γ X 1-γ . Here, X denotes one or more elements selected from a group consisting of O, Al, Si, Ga, Mo, Ag, and Au, and γ satisfies 0&lt;γ&lt;1.

CROSS-REFERENCE TO RELATED APPLICATIONS

This is a Continuation of application Ser. No. 15/988,707 filed May 24,2018, which in turn claims the benefit of priority from Japanese PatentApplication No. 2017404745, filed May 26, 2017. The disclosure of theprior application is hereby incorporated by reference herein in itsentirety.

TECHNICAL FIELD

The invention relates to a magnetoresistive effect element and alsorelates to a magnetic head, a sensor, a high-frequency filter, and anoscillator using the magnetoresistive effect element.

BACKGROUND

A giant magnetoresistive (GMR) effect element in the related artincludes a first ferromagnetic layer serving as a magnetization fixedlayer, a second ferromagnetic layer serving as a magnetization freelayer, and a nonmagnetic spacer layer that is disposed between the firstferromagnetic layer and the second ferromagnetic layer. That is, a GMReffect element has a structure of ferromagnetic layer/nonmagnetic spacerlayer/ferromagnetic layer. The GMR effect element can allow electronshaving a spin to pass therethrough in a state in which the magnetizationdirections of the upper and lower ferromagnetic layers are aligned. Acurrent-perpendicular-to-the plane (CPP) GMR effect element in therelated art has a smaller magnetoresistive effect than a tunnelingmagnetoresistive (TMR) effect element. Accordingly, in a GMR effectelement disclosed in Patent Reference 1, a Heusler alloy (Co₂(Fe, Mn)Si)is used for the ferromagnetic layers and Ag is used for the nonmagneticspacer layer, whereby improvement in a magnetoresistive effect isattempted.

Japanese Patent Laid-Open Application No. 2012-190914.

SUMMARY

However, according to the knowledge of the inventors of the invention,the magnetoresistive effect in a magnetoresistive effect element inwhich a Heusler alloy and a nonmagnetic metal are simply combined is notsatisfactory.

The invention is made in consideration of the above-mentioned problemand an object thereof is to provide a magnetoresistive effect elementwith an improved magnetoresistive effect.

In order to achieve the above-mentioned object, there is provided afirst magnetoresistive effect element including: a first ferromagneticlayer (that serves as a magnetization fixed layer; a secondferromagnetic layer that serves as a magnetization free layer; and anonmagnetic spacer layer that is disposed between the firstferromagnetic layer and the second ferromagnetic layer, wherein thenonmagnetic spacer layer includes a nonmagnetic metal layer that isformed of Ag, and at least one of a first insertion layer that isdisposed on a bottom surface of the nonmagnetic metal layer and a secondinsertion layer that is disposed on a top surface of the nonmagneticmetal layer, and wherein the first insertion layer and the secondinsertion layer include an Fe alloy that is expressed by General Formula(1):

Fe_(γ)X_(1-γ)  (1)

(where X denotes one or more elements selected from a group consistingof O, Al, Si, Ga, Mo, Ag, and Au, and γ satisfies 0<γ<1).

In this case, since lattice matching between one insertion layerincluding an Fe alloy and the nonmagnetic metal layer including Ag isenhanced and lattice matching with the ferromagnetic layer locatedoutside the insertion layer can be enhanced, a magnetoresistive effectis improved.

In a second magnetoresistive effect element, γ in General Formula (1)may satisfy 0.65≤γ≤0.9. In this case, when the content of Fe in the Fealloy is within the above-mentioned range (0.65≤γ≤0.9), the MR ratio ishigher than when the content of Fe is outside of this range.

In a third magnetoresistive effect element, at least one of the firstferromagnetic layer and the second ferromagnetic layer may include aHeusler alloy that is expressed by General formula (2):

Co₂L_(α)M_(β)  (2)

(where L denotes one or more elements selected from a group consistingof Mn and Fe, M denotes one or more elements selected from a groupconsisting of Si, Al, Ga, and Ge, 0.75≤α≤1.6 is satisfied, and0.65≤β≤1.35).

In a fourth magnetoresistive effect element, X in General formula (1)may be one or more elements selected from a group consisting of Al, Si,and Ga. When such an element and an Fe alloy are used, it is possible toachieve a high MR ratio.

In a fifth magnetoresistive effect element, α and β in General formula(2) may satisfy 2≤α+β≤2.6. In this range (2≤α+β≤2.6), it is possible toacquire a high MR ratio. When α and β in General formula (2) satisfy0.85≤α≤1.55, 0.75≤β≤1.25, and 0.2≤α+β≤2.55, it is possible to achieve ahigh MR ratio.

In the magnetoresistive effect element, 0.2 nm≤t1≤10 nm may be satisfiedwhere t1 denotes a thickness of the first insertion layer, and 0.2nm≤t2≤10 nm may be satisfied where t2 denotes a thickness of the secondinsertion layer. In this case, it is possible to achieve a high MRratio.

Preferably, when 0.5 nm≤t1≤8 nm and 0.5 nm≤t2≤8 nm are satisfied, it ispossible to achieve a high MR ratio.

A magnetic head, a sensor, a high-frequency filter, and an oscillatorthat include the above-mentioned magnetoresistive effect element have alarge magnetoresistive effect and thus excellent characteristics due tothe magnetoresistive effect can be exhibited.

With the magnetoresistive effect element according to the invention, itis possible to improve a magnetoresistive effect.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front view of a magnetoresistive effect element MR accordingto an example; FIG. 2 is a front view of a magnetoresistive effectelement MR according to a comparative example;

FIG. 3 is a table illustrating a relationship between an Fe content γ inan insertion layer formed of Fe_(γ)X_(1-γ) and a standardized MR ratio;

FIG. 4 is a graph in which data illustrated in FIG. 3 is plotted;

FIG. 5 is a table illustrating a standardized MR ratio and the like inGMR effect elements (a comparative example and Examples 1 to 5) whenvarious materials are used;

FIG. 6 is a table illustrating a standardized MR ratio and the like inGMR effect elements (Example A group) when various materials are used;

FIG. 7 is a table illustrating a standardized MR ratio and the like inGMR effect elements (Example B group) when various materials are used;

FIG. bis a graph illustrating a relationship between a sum (α+β) ofcontents of elements other than Co in a ferromagnetic layer and astandardized MR ratio when materials of Example A group and Example Bgroup are used;

FIG. 9 is a graph illustrating a relationship between a content α of anL element in a ferromagnetic layer and a standardized MR ratio whenmaterials of Example A group are used;

FIG. 10 is a graph illustrating a relationship between a content β of anM element in a ferromagnetic layer and a standardized MR ratio whenmaterials of Example B group are used;

FIG. 11 is a table illustrating a thickness of an insertion layer, astandardized MR ratio, and the like when materials of Example C groupare used;

FIG. 12 is a graph illustrating a relationship between a thickness of aninsertion layer and a standardized MR ratio when materials of Example Cgroup are used;

FIG. 13 is a table illustrating lattice constants, structure types, andPearson symbols of Ag and Fe alloys;

FIG. 14 is a table illustrating a lattice constant of various Heusleralloys;

FIG. 15 is a table illustrating a lattice mismatching ratio between anAg or Fe alloy and various Heusler alloys;

FIG. 16 is a table illustrating a lattice mismatching patio between anAg or Fe alloy and various Heusler alloys;

FIG. 17 is a diagram illustrating a sectional configuration of areproduction unit of a magnetic head including a magnetoresistive effectelement;

FIG. 18 is a diagram illustrating a sectional configuration of amagnetic head including a magnetoresistive effect element;

FIG. 19 is a diagram illustrating a structure of a current sensorincluding a plurality of magnetoresistive effect elements; and

FIG. 20 is a diagram illustrating a structure of a high-frequency filterincluding a plurality of magnetoresistive effect elements.

DETAILED DESCRIPTION

Hereinafter, a magnetoresistive effect element according to anembodiment of the invention will be described. The same elements will bereferenced by the same reference signs and description thereof will notbe repeated. When a three-dimensional orthogonal coordinate system isused, a thickness direction of each layer is defined as a. Z axis andtwo orthogonal axes perpendicular to the Z axis are defined as an X axisand a Y axis.

FIG. 1 is a front view of a magnetoresistive effect element MR accordingto an example.

A magnetoresistive effect element MR sequentially includes a firstnonmagnetic metal layer 2, and a second nonmagnetic metal layer 3 on afirst base layer 1. Thereon, a first ferromagnetic layer 4 serving as amagnetization fixed layer, a nonmagnetic spacer layer 5, and a secondferromagnetic layer 6 serving as a magnetization free layer aresequentially stacked. A cap nonmagnetic metal layer 7 and a contactmetal layer 8 are sequentially formed on the second ferromagnetic layer6. When a bias is applied between the first nonmagnetic metal layer 2 orthe second nonmagnetic metal layer 3 located in the lower part and thecontact metal layer 8 located in the upper part, electrons having a spinin a specific direction can be allowed to pass therethrough in adirection perpendicular to a layer surface.

When magnetization directions in the magnetization fixed layer and themagnetization free layer are the same direction (for example, the +Xdirection and the +X direction) (parallel), electrons of which the spindirection is parallel thereto pass through the layer surfaces in theperpendicular direction. When the magnetization directions in themagnetization fixed layer and the magnetization free layer are oppositeto each other (for example, the +X direction and the −X direction)(antiparallel), electrons having a spin of which the direction isopposite to the magnetization direction are reflected and do not passthrough the layer surfaces.

Since the magnetization direction of the first ferromagnetic layer 4(the magnetization fixed layer) is fixed and the magnetization directionof the second ferromagnetic layer 6 (the magnetization free layer) canbe changed depending on an external magnetic field, an amount ofelectrons passing through varies depending on the magnitude of theexternal magnetic field. A resistance is low when the amount ofelectrons passing through is large, and a resistance is high when theamount of electrons passing through is small. Since the firstferromagnetic layer 4 serving as the magnetization fixed layer has athickness larger than that of the second ferromagnetic layer 6 and themagnetization direction thereof is less likely to be changed dependingon the external magnetic field than that of the second ferromagneticlayer 6, the first ferromagnetic layer 4 serves as a magnetization fixedlayer in which the magnetization direction is substantially fixed.

In FIG. 1, representative material names are shown in the layers for thepurpose of easy understanding, but other materials are applicable to thelayers.

The nonmagnetic spacer layer 5 is disposed between the firstferromagnetic layer 4 and the second ferromagnetic layer 6. Thenonmagnetic spacer layer 5 includes a nonmagnetic metal layer 5B formedof Ag and at least one of a first insertion layer 5A disposed on thebottom surface of the nonmagnetic metal layer 5B and a second insertionlayer 5C disposed on the top surface of the nonmagnetic metal layer 5B.That is, a structure in which one of the first insertion layer 5A andthe second insertion layer 5C is omitted and the central nonmagneticmetal layer 5B comes in contact with one of the upper and lowerferromagnetic layers may be employed.

The first insertion layer 5A and the second insertion layer 5C includean Fe alloy which is expressed by General formula (1).

Fe_(γ)X_(1-γ)  (1)

Here, X denotes one or more elements selected from a group consisting ofO, Al, Si, Ga, Mo, Ag, and Au, and γ satisfies 0<γ<1.

That is, in addition to Fe alloys which arc combinations such as Fe—O,Fe—Al, Fe—Si, Fe—Ga, Fe—Mo, Fe—Ag, and Fe—Au, Fe alloys such as Fe—Al—Siand Fe—Al—Mo which are close thereto in electrical properties andlattice constant of crystal structure can also be used.

In this case, since lattice matching between one insertion layer (thefirst insertion layer 5A or the second insertion layer 5C) including anFe alloy and the nonmagnetic metal layer 5B including Ag can be enhancedand lattice matching between the insertion layer (the first insertionlayer 5A or the second insertion layer 5C) and the ferromagnetic layer(the first ferromagnetic layer 4 or the second ferromagnetic layer 6)located outside thereof can be enhanced, it is possible to improve amagnetoresistive effect.

Materials and thicknesses (suitable ranges) of the layers are asfollows.

-   -   Contact metal layer 8: Ru, 5 nm, (range of 3 nm to 8 nm)    -   Cap nonmagnetic metal layer 7: Ag, 5 nm, (range of 3 nm to 8    -   Second ferromagnetic layer 6: CMS (cobalt-manganese-silicon        alloy), 5 nm, (range of 3 nm to 20 nm)    -   Second insertion layer 5C: Fe alloy (Fe_(γ)X_(1-γ) described        above), 0.5 nm, (range of 0.2 nm to 10 nm)    -   Nonmagnetic metal layer 5B: Ag, 5 nm, (range of 3 nm to 10 nm)    -   First insertion layer 5A: Fe alloy (Fe_(γ)X_(1-γ) described        above), 0.5 nm, (range of 0.2 nm to 10 nm)    -   First ferromagnetic layer 4: CMS (a cobalt-manganese-silicon        alloy), 10 nm, (range of 3 nm to 20 nm)    -   Second nonmagnetic metal layer 3: Ag, 50 nm, (range of 20 nm to        100 nm)    -   First nonmagnetic metal layer 2: Cr, 20 nm, (range of 10 nm to        30 nm)    -   First base layer 1: MgO, 0.5 mm, (range of 0.1 mm to 2 mm)

Examples of the materials of the layers constituting themagnetoresistive effect element will be described in more detail.

Ru can be suitably used for the contact metal layer 8, and the contactmetal layer 8 may additionally include one or more metal elements fromRu, Ag, Al, Cu, Au, Cr, Mo, Pt, W, Ta, Pd, and Ir, an alloy of thesemetal elements, or a stacked structure of materials including two ormore types of these metal elements.

Ag can be suitably used for the cap metal layer 7, and the cap metallayer 7 may additionally include one or more metal elements from Ru, Ag,Al, Cu, Au, Cr, Mo, Pt, W, Ta, Pd, and Ir, an alloy of these metalelements, or a stacked structure of materials including two or moretypes of these metal elements.

CMS (Co₂L_(α)M_(β)) which is a Heusler alloy can be suitably used forthe second ferromagnetic layer 6, and the second ferromagnetic layer 6may include Heusler alloys such as Co₂MnGe, Co₂MnGa, Co₂FeGa, Co₂FeSi,Co₂MnSn, Co₂MnAl, Co₂FeAl, Co₂CrAl, Co₂VAl, Co₂MnGaSn, Co₂FeGeGa,Co₂MnGeGa, Co₂FeGaSi, Co₂FeGeSi, Co₂CrIn, and Co₂CrSn or ferromagneticmaterials such as Fe₃O₄, CrO₂, and CoFeB or may be substantially formedof these ferromagnetic materials. Co₂L_(α)M_(β) denotes that theproportion of the number of atoms of L constituting the whole alloy is αand the proportion of the number of atoms of M is β when the number ofatoms of Co is defined as two.

CMS (Co₂L_(α)M_(β)) which is a Heusler alloy can be suitably used forthe first ferromagnetic layer 4, and the first ferromagnetic layer 4 mayinclude Heusler alloys such as Co₂MnGe, Co₂MnGa, Co₂FeGa, Co₂FeSi,Co₂MnSn, Co₂MnAl, Co₂FeAl, Co₂CrAl, Co₂MnGaSn, Co₂FeGeGa, Co₂MnGeGa,Co₂FeGaSi, Co₂FeGeSi, Co₂CrIn, and Co₂CrSn or ferromagnetic materialssuch as Fe₃O₄, CrO₂, and CoFeB or may be substantially formed of theseferromagnetic materials.

Ag can be suitably used for the second nonmagnetic metal layer 3, andthe second nonmagnetic metal layer 3 may include at least one metalelement from, for example, Ag, Au, Cu, Cr, V, Al, W, and Pt, an alloy ofthese metal elements, or a stacked structure of materials including twoor more types of these metal elements. Examples of an alloy of the metalelements include an AgZn alloy, an AgMg alloy, and a NiAl alloy of acubic type.

Cr can be suitably used for the first nonmagnetic metal layer 2, and thefirst nonmagnetic metal layer 2 may include at least one metal elementfrom, for example, Ag, Au, Cu, Cr, V, Al, W, and Pt, an alloy of thesemetal elements, or a stacked structure of materials including two ormore types of these metal elements. Examples of an alloy of the metalelements include an AgZn alloy, an AgMg alloy, and a NiAl alloy of acubic type.

MgO can be suitably used for the first base layer 1, and the material ofthe first base layer 1 is not particularly limited as long as it is amaterial having an appropriate mechanical strength and being suitablefor heating or fine machining such as metal oxide single crystalsubstrates, silicon single crystal substrates, silicon single crystalsubstrates with a thermal oxide film, sapphire single crystalsubstrates, ceramics, quartz, and glass. With a substrate including MgOsingle crystal substrates, an epitaxial growth film is easily formed.Characteristics of high magnetoresistance can be exhibited with thisepitaxial growth film.

The superiority of the above-mentioned structure to a comparativeexample will be described below.

FIG. 2 is a front view of a magnetoresistive effect element MR accordingto a comparative example.

The magnetoresistive effect element according to the comparative examplehas a basic structure in which the insertion layers of an Fe alloy (thefirst insertion layer 5A and the second insertion layer 5C) are removedfrom the structure illustrated in FIG. 1, and the other structuresthereof are the same as illustrated in FIG. 1 (the same as the structureof the exemplary example). In the comparative example, Co_(0.5)Fe_(0.5)is used instead of CMS as the material of the first ferromagnetic layer4 and the second ferromagnetic layer 6.

An MR ratio is used as an index for evaluating the performance of amagnetoresistive effect element. The MR ratio is given as [(resistancevalue of element when magnetization direction is antiparallel−resistancevalue of element when magnetization direction is parallel)/resistancevalue of element when magnetization direction is parallel].

The MR ratios in subsequent examples are standardized with respect tothe MR ratio in this comparative example (comparative example 1 in FIG.5) as a reference (=1).

FIG. 3 is a table illustrating a relationship between the content of Feγ in an insertion layer formed of Fe_(γ)X_(1-γ) and the standardized MRratio in the structure of the embodiment (the structure in the exemplaryembodiment), and FIG. 4 is a graph in which data illustrated in FIG. 3are plotted.

FIGS. 3 and 4 illustrate results when Co_(0.5)Fe_(0.5) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 in thestructure in the embodiment illustrated in FIG. 1, and the standardizedMR ratio is equal to or greater than 1 irrespective of which one of O,Al, Si, Ga, Mo, Ag, and Au is used as the X element of Fe_(γ)X_(1-γ). Itcan be seen that γ in General formula (1) (Fe_(γ)X_(1-γ)) preferablysatisfies 0.6≤γ≤0.9. When γ is in this range, the standardized MR ratiois equal to or greater than 2.7 and equal to or less than 4.7 and ismuch greater than the MR ratio in the comparative example.

In this way, when the content of Fe in the Fe alloy is in the range(0.6≤γ≤0.9), the MR ratio is higher than that when the content of Fe isoutside of this range.

FIG. 5 is a table illustrating the standardized MR ratio and the like inGMR elements (the comparative example and Examples 1 to 5) when variousmaterials are used.

As Comparative example 1, the above-mentioned comparative example (theexample in which Co_(0.5)Fe_(0.5) is used for the first ferromagneticlayer 4 and the second ferromagnetic layer 6) is illustrated, and thestandardized MR ratio is obtained by standardization with the MR ratioat that time as 1, In Comparative example 1, when CMS(Co₂Mn_(1.0)Si_(0.92)) is used as the material of the firstferromagnetic layer 4 and the second ferromagnetic layer 6, thestandardized MR ratio is 4.8.

Example 1 is an example in which Co_(0.5)Fe_(0.5) is used for the firstferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.2)Au_(0.8) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas in the exemplary embodiment illustrated in FIG. 1.

Example 2 is an example in which Co_(0.5)Fe_(0.5) is used for the firstferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.65)Au_(0.35) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas in the exemplary embodiment illustrated in FIG. 1.

Example 3 is an example in which Co₂Mn_(1.0)Si_(0.92) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.65)Au_(0.35) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1, The other materials and structures are the sameas in the exemplary embodiment illustrated in FIG. 1.

Example 4 is an example in which Co₂Mn_(1.0)Si_(0.92) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.75)Al_(0.25) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1, The other materials and structures are the sameas in the exemplary embodiment illustrated in FIG. 1.

Example 5 is an example in which Co₂Mn_(1.3)Si_(0.92) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.75)Al_(0.25) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas in the exemplary embodiment illustrated in FIG. 1.

The magnitude of the standardized MR ratio in Comparative example 1 isthe smallest, and the standardized MR ratio in Example 1 using aninsertion layer is larger than the standardized MR ratio in Comparativeexample 1. It can be seen that the MR ratio is increased by using theinsertion layer.

In comparison with Example 1, the standardized MR ratio is larger inExample 2 in which the content of Fe (γ=0.65) in the insertion layer hasincreased. Accordingly, it is preferable that 0.6≤γ is satisfied inFe_(γ)X_(1-γ). Even with 0.6≤γ, there is an effect of an increased MRratio. This is because the first insertion layer and/or the secondinsertion layer can easily adopt a cubic crystal structure and thus thenonmagnetic spacer layer and the first ferromagnetic layer and/or thesecond ferromagnetic layer can be stacked with a higher crystal quality,whereby a larger magnetoresistive effect is exhibited. With 0.65≤γ, amore stable cubic crystal structure can be adopted.

In comparison with Example 2, the standardized MR ratio is larger inExample 3 in which the type of the ferromagnetic layer has been changedto a Heusler alloy (Co₂MnSi).

In comparison with Example 3, the standardized MR ratio is larger inExample 4 in which the material of the insertion layer has been changedfrom Au to Al.

In comparison with Example 4, the standardized MR ratio is larger inExample 5 in which the content of Mn in the ferromagnetic layer is setto be larger.

When Co₂L_(α)M_(β) is used for the first ferromagnetic layer 4 and thesecond ferromagnetic layer 6, L in the formula denotes one or moreelements from Mn and Fe and M denotes one or more elements selected fromthe group consisting of Si, Al, Ga, and Ge. Values of α+β, α(Mn) of Mn,and β(Si) of Si are also illustrated in FIG. 5.

FIG. 6 is a table illustrating the standardized. MR ratios and the likein GMR effect elements (Example A group) when various materials areused.

Example A group is an example in which Co₂Mn_(α)Si_(β) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.75)Al_(0.25) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas illustrated in FIG. 1. In Example A group, α changes from 0.45 to1.75 and β is fixed to 0.95.

FIG. 7 is a table illustrating the standardized MR ratios and the likein GMR effect elements (Example B group) when various materials areused.

Example B group is an example in which Co₂Mn_(α)Si_(β) is used for thefirst ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.75)Al_(0.25) with a thickness of 0.5 nm is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas illustrated in FIG. 1. In Example B group, α is fixed to 1.3 and βchanges from 0.55 to 1.45.

FIG. 8 is a graph illustrating a relationship between the sum (α+β) ofthe contents of elements other than Co in the ferromagnetic layer andthe standardized MR ratios when the materials of Example A group andExample B group are used.

When L in General formula (2): (Co₂L_(α)M_(β)) is set to Mn, M is set toSi, and 2≤α+β≤2.6 is satisfied, a high MR ratio can be obtained. InExample A, the MR ratio increases when α+β is equal to or greater than2. In Example A group, when α+β reaches 2.6, the MR ratio has a valuewhich is less than that when α+β is equal to 2.5 and greater than thatwhen α+β is equal to or greater than 2.7. When 2≤α+β≤2.55 and 2≤α+β≤2.5are satisfied, the MR ratio becomes greater.

Even in combinations of elements other than the case in which L is Mnand M is Si, defects in which a Co atom occupies an L site or an M siteare minimized. It is thought that the same relationships are establishedfor the reason that half metal characteristics of the firstferromagnetic layer 4 and the second ferromagnetic layer 6 are notimpaired.

Particularly, when L in General formula (Co₂L_(α)M_(β)) of theferromagnetic layer denotes one or more elements selected from the groupconsisting of Mn and Fe and M denotes one or more elements selected fromthe group consisting of Si, Al, Ga, and Ge, the lattice constants offerromagnetic layer/Fe alloy/Ag or values of the square roots thereofcan become close to each other as illustrated in FIGS. 15 and 16 whichwill be described later and it is thus considered that the MR ratio willbe able to be increased.

The first ferromagnetic layer 4 and the second ferromagnetic layer 6 areboth Heusler alloys which are expressed by General formula (2):(Co₂L_(α)M_(β)). It is thought that the increase in the MR ratio alsoresults from lattice matching, and when at least one of the firstferromagnetic layer 4 and the second ferromagnetic layer 6 satisfies theconditions described in the examples, it is thought that an increase inMR ratio will be caused.

Since the increase in the MR ratio also results from lattice matching,it is considered that an increase in the MR ratio is caused when atleast one of the first insertion layer 5A and the second insertion layer5C satisfies the conditions described in the examples.

FIG. 9 is a graph illustrating a relationship between the content ofelement L α in the ferromagnetic layer and the standardized MR ratiowhen the materials of Example A group are used.

In Example A group, α changes in the range of 0.45 to 1.75. When α isequal to or greater than 0.85, the MR ratio increases rapidly. When α isequal to 0.65, the MR ratio does not have a large value but is greaterthan that when α has a lower value. Accordingly, when α≤0.65 issatisfied, α<0.65 is satisfied, and α is greater than 0.7 which is amedian value between 0.65 and 0.85, the MR ratio is considered to behigh. When α is equal to or less than 1.55, the MR ratio remains high.When α is equal to 1.65, the MR ratio does not have a large value but isgreater than that when α has a greater value. Accordingly, α≤1.65 ispreferable, α<1.65 is more preferable, and the MR ratio is considered tobe high when α is less than 1.6 which is a median value between 1.55 and1.65, that is, when α≤1.55 is satisfied. In this way, in at least therange of 0.7≤α≤1.6, the MR ratio is considered to be high.

That is, regarding the materials of the ferromagnetic layer, when L inGeneral formula (2): (Co₂L_(α)M_(β)) denotes Mn and M denotes Si andwhen 0.65≤α≤1.65 is satisfied, a high MR ratio can be achieved. When0.85≤α≤1.55 is satisfied, a higher MR ratio can be achieved. Even incombinations of elements other than the case in which L is Mn and M isSi, defects in which a Co atom occupies an L site or an M site areminimized. It is thought that the same relationships are established forthe reason that half metal characteristics of the first ferromagneticlayer 4 and the second ferromagnetic layer 6 are not impaired. L denotesone or more elements selected from the group consisting of Mn and Fe,and the lattice constant when L includes two or more elements canapproximately have, for example, a median value between the latticesconstants of the elements. In consideration that an increase in the MRratio also results from lattice matching, it is thought that the sameeffects would be able to be achieved even when two or more elements areused.

M denotes one or more elements selected from the group consisting of Si,Al, Ga, and Ge, and the lattice constant when L includes two or moreelements can approximately have, for example, a median value of thelattices constants of the elements. In consideration that an increase inthe MR ratio also results from lattice matching, it is thought that thesame effects would be able to be achieved even when two or more elementsare used for M.

FIG. 10 is a graph illustrating a relationship between the content ofelement M β in the ferromagnetic layer and the standardized MR ratiowhen the materials of Example B group are used.

In Example B group, β changes in the range of 0.55 to 1.45. When β isequal to or greater than 0.75, the MR ratio increases rapidly. When β isequal to 0.65, the MR ratio does not have a large value but is greaterthan that when β has a lower value. Accordingly, 0.65≤β is preferable,0.65<β is more preferable, it is still more preferable that β is greaterthan 0.7 which is a median value between 0.65 and 0.85, and 0.75≤β isstill more preferable, whereby it is considered that the MR ratio willbe high. When β is equal to or less than 1.25, the MR ratio remains at alarge value. When β is equal to 1.35, the MR ratio does not have a largevalue but the MR ratio is greater than that when β is greater.Accordingly, β≤1.35 is preferable, β<1.35 is more preferable, β<1.3which is a median value between 1.25 and 1.35 is still more preferable,and β≤1.25 is still more preferable, whereby the MR ratio increases.

That is, regarding the materials of the ferromagnetic layer, when L inGeneral formula (2): (Co₂L_(α)M_(β)) denotes Mn and M denotes Si andwhen 0.65≤β≤1.35 is satisfied, a high. MR ratio can be achieved.

As described above, from the viewpoint of an increase in the MR ratio,0.65≤α≤1.65 is preferable, and 0.65<α, 0.7<α, and 0.85≤α are preferableregarding the lower limit. Regarding the upper limit, in comparison withα≤1.65, α<1.65, α<1.6, and α≤1.55 are more preferable. From theviewpoint of an increase in the MR ratio, 0.65≤β≤1.35 is preferable, and0.65<β, 0.7<β, and 0.75≤β are more preferable regarding the lower limit.Regarding the upper limit, in comparison with α≤1.35, β<1.35, β<1.3, andβ≤1.25 are more preferable.

Even in combinations of elements other than the case in which L is Mnand M is Si, defects in which a Co atom occupies an L site or an M siteare minimized. It is thought that the same relationships are establishedfor the reason that half metal characteristics of the firstferromagnetic layer 4 and the second ferromagnetic layer 6 are notimpaired.

FIG. 11 is a table illustrating the thickness of the insertion layer,the standardized MR ratio, and the like when the materials of Example Cgroup are used, and FIG. 12 is a graph illustrating a relationshipbetween the thickness of the insertion layer and the standardized MRratio when the materials of Example C group are used.

Example C group is an example in which Co₂Mn_(1.3)Si_(0.92) is used forthe first ferromagnetic layer 4 and the second ferromagnetic layer 6 andFe_(0.75)Al_(0.25) with a thickness of t (nm) is used for the firstinsertion layer 5A and the second insertion layer 5C in the structureillustrated in FIG. 1. The other materials and structures are the sameas illustrated in FIG. 1. In Example C group, α is fixed to 1.3 and β isfixed to 0.92.

The thicknesses t of two insertion layers change in the range of 0.1 nmto 15 nm. The MR ratio increases when the thickness t of the insertionlayer is equal to or greater than 0.2 nm, and the MR ratio when thethickness t of the insertion layer is equal to or less than 10 nm isseveral numerical stages greater than the MR ratio when the thickness is12 nm. Accordingly, 0.2 nm should be satisfied where t1 denotes thethickness of the first insertion layer 5A, and 0.2 nm≤t2≤10 nm should besatisfied where t2 denotes the thickness of the second insertion layer5C. In this case, a high MR ratio can be achieved.

Regarding the thicknesses t (t1 and t2) of the insertion layers, 0.2nm≤t≤8 nm is more preferable (0.2 nm≤t1≤8 nm and 0.2 nm≤t2≤8 nm). In theranges of 0.2 nm<t1 and 0.2 nm<t2, since the thicknesses are equal to orgreater than a unit lattice in a crystal structure, a film with a layershape can be easily formed. 0.5 nm≤t≤8 nm is more preferable (0.5nm≤t1≤8 nm and 0.5 nm≤t2≤8 nm). In this case, a high MR ratio can beachieved.

The lattice constants of the layers will be described below.

FIG. 13 is a table illustrating lattice constants, structure types, andPearson symbols of Ag and Fe alloys.

The nonmagnetic metal layer 5B illustrated in FIG. 1 is formed of Ag andthe first insertion layer 5A and the second insertion layer 5C areformed of Fe_(γ)X_(1-γ), where X is selected from the group consistingof O, Al, Si, Ga, Mo, Ag, and Au. X may include one element or two ormore elements (X1 and X2) among these elements. In the latter case, thelattice constant can approximately have, for example, a median valuebetween the lattice constant when X1 is used and the lattice constantwhen X2 is used.

Fe_(γ)X_(1-γ) denotes an Fe alloy and thus γ is in the range of 0<γ<1.

In FIG. 13, the lattice constants a of Fe_(0.5)O_(0.5),Fe_(0.1)Al_(0.9), Fe_(0.75)Al_(0.25), Fe_(0.75)Si_(0.25), Fe_(0.75)Ga_(0.25), Mo_(0.73)Fe_(0.27), Ag_(0.5)Fe_(0.5), and Au_(0.5)Fe_(0.5),square roots thereof, structure types of crystals, and Pearson symbolsthereof are illustrated. When the insertion layers (5A and 5C) growwhile rotating by 45° with respect to the vertical crystal axes of theneighboring ferromagnetic layers (4, and 6), a value obtained bymultiplying a by a square root of 2 approaches the lattice constant ofthe ferromagnetic layer. The mark (*) in the figure denotes a valuewhich approaches the lattice constants of the ferromagnetic layers (4and 6), and a marked by (*) or a value obtained by multiplying a by asquare root of 2 is selected for lattice matching.

FIG. 14 is a table illustrating the lattice constants of theferromagnetic layers (4 and 6) (various Heusler alloys).

In the figure, the lattice constants a of Co₂MnSi, Co₂MnGe, Co₂MnGa,Co₂FeGa, Co₂FeSi, Co₂MnSn, Co₂MnAl, Co₂FeAl, Co₂CrAl, Co₂VAl,Co₂MnGa_(0.5)Sn_(0.5), and Co₂FeGeGa are illustrated. FIGS. 15 and 16are tables illustrating lattice mismatching ratios between Ag (thenonmagnetic metal layer) or Fe alloys (the insertion layers) illustratedin FIG. 13 and various Heusler alloys (the ferromagnetic layer)illustrated in FIG. 14.

Lattice mismatching ratio=[(lattice constant a of Ag or insertion layeror value obtained by multiplying a by square root of 2−lattice constantof ferromagnetic layer)/lattice constant of ferromagnetic layer]

In combinations of the materials, when the lattice mismatching ratio issmall, the MR ratio can be set to be large. Specifically, the MR ratiocan be increased by providing an Fe alloy (the insertion layer) in whichthe lattice mismatching ratio is less than the lattice mismatching ratiobetween Ag (the nonmagnetic metal layer) and various Heusler alloys (theferromagnetic layer), and the MR ratio can be further increased byproviding an Fe alloy (the insertion layer) in which the latticemismatching ratio between Ag (the nonmagnetic metal layer) and variousHeusler alloys (the ferromagnetic layer) can be increased by 0.5% ormore. However, since the stacking is stacking between dissimilarmaterials, the absolute value of the lattice mismatching ratio isgreater than zero. The lattice constant refers to a value at roomtemperature (300 K).

FIG. 17 is a diagram illustrating a sectional configuration of areproduction unit of a magnetic head including a magnetoresistive effectelement.

The magnetic head includes the magnetoresistive effect element MRillustrated in FIG. 1. Specifically, the magnetic head includes a lowermagnetic shield 21, a magnetoresistive effect element MR that is fixedto the lower magnetic shield, an upper magnetic shield 22 that is fixedto the top of the magnetoresistive effect element MR, and a sidemagnetic shield 23 that is fixed to the side of the upper magneticshield 22, The magnetic shields are formed of NiFe or the like. Themagnetic head having such a structure is known and an example thereof isdescribed in U.S. Pat. No. 5,695,697, which can be referred to.

FIG. 18 is a diagram illustrating a sectional configuration of amagnetic recording head including a magnetoresistive effect element MR.

The magnetic recording head includes a main magnetic pole 61, acirculation magnetic pole 62, and a spin torque oscillator (anoscillator) 10 that is disposed in parallel with the main magnetic pole61. The spin torque oscillator 10 has the same structure as theabove-mentioned magnetic head, that is, a structure in which the lowermagnetic shield 21 and the upper magnetic shield 22 are disposed aselectrodes on the top and bottom of the magnetoresistive effect elementMR.

Since a coil 63 is wound on a base end portion of the main magnetic pole61, a writing magnetic field is generated around the main magnetic pole61 when a driving current is supplied to a current source I_(R). Thegenerated magnetic field passes through the magnetic poles to form aclosed magnetic circuit.

When a DC current flows across the upper and lower electrodes of thespin torque oscillator 10 including the magnetoresistive effect elementMR, ferromagnetic resonance is generated due to a spin torque generatedin a spin injection layer, and a high-frequency magnetic field isgenerated from the spin torque oscillator 10. High-density magneticrecording is performed on a magnetic recording medium 80 facing themagnetic fields only in a portion in which the recording magnetic fieldresulting from the main magnetic pole 61 and the high-frequency magneticfield resulting from the spin torque oscillator 10 overlap each other. Amagnetic recording head having such a structure is known and an examplethereof is described in Japanese Patent No, 5173750, which can bereferred to.

FIG. 19 is a diagram illustrating a structure of a current sensorincluding a plurality of magnetoresistive effect elements.

The current sensor is configured as a bridge circuit in which aplurality of magnetoresistive effect elements MR are electricallyconnected. In the drawing, a bridge circuit is configured by fourmagnetoresistive effect elements MR, and two circuit arrays in which twomagnetoresistive effect elements MR are connected in series areconnected in parallel between the ground potential and the sourcepotential Vdd. Junction points between two magnetoresistive effectelements MR in the circuit arrays serve as a first output terminal Out1and a second output terminal Out2, and a voltage therebetween is anoutput signal.

When it is assumed that a wire to be measured extends in the Z axisdirection, a magnetic field is generated around the wire and resistancevalues of the magnetoresistive effect elements MR vary depending on themagnitude of the magnetic field. Since the intensity of the outputsignal depends on the magnitude of the magnetic field, that is, anamount of current flowing in the wire, this device can function as acurrent sensor. This device also functions directly as a magnetic sensorthat detects the magnitude of the magnetic field.

FIG. 20 is a diagram illustrating a structure of a high-frequency filterincluding a plurality of magnetoresistive effect elements.

The high-frequency filter has a structure in which a plurality ofmagnetoresistive effect elements MR are electrically connected inparallel. That is, upper electrodes (shield electrodes or contactelectrodes) of the magnetoresistive effect elements MR are connected ormade common and lower electrodes (shield electrodes or first nonmagneticmetal layers) of the magnetoresistive effect elements MR are connectedor made common.

A plurality of magnetoresistive effect elements MR have differenthorizontal sectional areas (sectional areas in the XY plane) and thushave different resonance frequencies. When a high-frequency signal isinput from an input terminal In, each magnetoresistive effect element MRabsorbs a signal component of the same frequency as the resonancefrequency thereof in the input high frequency signal, and the remaininghigh-frequency signal component is output from an output terminal Out.Accordingly, this device functions as a high-frequency filter. A devicehaving such a structure is known and an example thereof is described inPCT International Publication No. WO2011/033664, which can be referredto.

The magnetoresistive effect element illustrated in FIG. 1 can bemanufactured as follows.

First, the first nonmagnetic metal layer 2, the second nonmagnetic metallayer 3, the first ferromagnetic layer 4, the nonmagnetic spacer layer5, the second ferromagnetic layer 6, the cap nonmagnetic metal layer 7,and the contact metal layer 8 are sequentially deposited on the firstbase layer 1. The nonmagnetic spacer layer 5 is formed by depositing thefirst insertion layer 5A, the nonmagnetic metal layer 5B, and the secondinsertion layer 5C on the first ferromagnetic layer 4.

A sputtering method which is a known technique is used for thisdeposition. In this example, the layers are formed by film formation atroom temperature using sputtering targets formed of the materials of thelayers and ultrahigh vacuum sputtering equipment, but two or moresputtering targets may be simultaneously used. That is, bysimultaneously sputtering two (or more) targets of different materials Aand B, the material contents of an alloy film of A and B or the layerscan be adjusted. For example, an alloy film can be formed by sputteringan Fe target and a different metal target together (simultaneously). AnFeO (oxygen) film can be formed by introducing oxygen gas into adeposition chamber of the sputtering equipment at the time of sputteringof Fe. Commercially available products can be used as the substratematerial, and MgO which is a commercially available product is used asthe first base layer. The first ferromagnetic layer 4 is annealed at500° C. after deposition. The second ferromagnetic layer 6 is annealedat 450° C. after deposition. The magnetoresistive effect element ismicrofabricated into a shape in which magnetoresistive characteristicscan be evaluated by electron beam lithography and Ar ion milling. Amethod of manufacturing CMS or the like using sputtering equipment isdescribed, for example, in U.S. Patent Application Publication No.2007/0230070, U.S. Patent Application Publication No. 2013/0229895, U.S.Patent Application Publication No. 2014/0063648, U.S. Patent ApplicationPublication No. 2007/0211391, and U.S. Patent Application PublicationNo. 2013/0335847.

As described above, with a magnetoresistive effect element satisfyingGeneral formula (1) and/or General formula (2), it is possible toachieve a high MR ratio. With a magnetic head, a sensor, ahigh-frequency filter, or an oscillator including the above-mentionedmagnetoresistive effect element, an excellent magnetoresistive effect isprovided. Accordingly, they can exhibit excellent characteristics basedthereon.

The first insertion layer and/or the second insertion layer can have astable cubic crystal structure. As a result, since the nonmagneticspacer layer and the first ferromagnetic layer and/or the secondferromagnetic layer can be stacked with a higher crystal quality, it ispossible to exhibit a better magnetoresistive effect.

Since α and β satisfy the above-mentioned ranges, the Heusler alloys ofthe first ferromagnetic layer and the second ferromagnetic layer haveclose lattice constants in stoichiometric compositions. As a result, itis possible to further reduce lattice mismatching between the firstferromagnetic layer and/or the second ferromagnetic layer and thenonmagnetic spacer layer and to exhibit a better magnetoresistiveeffect.

When an Fe alloy includes Al, Si, or Ga, it is possible to easily alignmagnetizable axis directions of the first insertion layer and/or thesecond insertion layer, the first ferromagnetic layer, and the secondferromagnetic layer. As a result, a magnetoresistive effect which isexhibited at a relative angle of magnetization between that of the firstferromagnetic layer and the second ferromagnetic layer can be maintainedat a maximum. An FeX alloy is a magnetic material, but crystals can growwithout rotating 45 degrees with respect to the Heusler alloy when X=Al,Si, or Ge.

When α+β is in the above-mentioned range, half metal characteristics ofthe Heusler alloys included in the first ferromagnetic layer and thesecond ferromagnetic layer can easily be maintained. As a result, it ispossible to achieve a much better magnetoresistive effect.

When the thickness of the first insertion layer is defined as t1 and thethickness of the second insertion layer is defined as t2, it ispreferable that t1 and t2 be set to be equal to or less than a spindiffusion length of the materials of the insertion layers. Since a spinsource in electrons which move from the first ferromagnetic layer to thesecond ferromagnetic layer is not affected by the first insertion layerand/or the second insertion layer, the magnetoresistive effect isenhanced. Specifically, when t1≤10 nm and/or t2≤10 nm in theabove-mentioned ranges of the thicknesses t1 and t2, spin-scattering ofelectrons that move between the first ferromagnetic layer 4 and thesecond ferromagnetic layer 6 can be satisfactorily suppressed in thefirst insertion layer and/or the second insertion layer during themovement of elements and thus the magnetoresistive effect isparticularly enhanced. When 0.2 nm≤t1 and/or 0.2 nm≤t2 are satisfied,the thicknesses of the first insertion layer and the second insertionlayer are sufficiently large and thus it is possible to satisfactorilyreduce lattice mismatching between the nonmagnetic spacer layer and thefirst ferromagnetic layer and/or the second ferromagnetic layer. As aresult, since the nonmagnetic spacer layer and the first ferromagneticlayer 4 and/or the second ferromagnetic layer 6 are stacked with a highcrystal quality, the magnetoresistive effect is particularly enhanced.

Since the behavior of the magnetoresistive effect element having theabove-mentioned structure with respect to spin is thought to occur inthe same way in a CIP-GMR effect element (a current-in-plane type GMReffect element) as well as in a CPP-GMR effect element in principle, theabove-mentioned structure is also considered to be effective in aCIP-GMR effect element from the viewpoint of improvement in MR ratio.This is because the crystallinity of the first ferromagnetic layerand/or the second ferromagnetic layer and the nonmagnetic spacer layeris improved due to reduction of the lattice mismatching ratio and thusan excellent magnetoresistive effect can be achieved.

What is claimed is:
 1. A magnetoresistive effect element comprising: afirst ferromagnetic layer; a second ferromagnetic layer; and a spacerlayer that is disposed between the first ferromagnetic layer and thesecond ferromagnetic layer, wherein the spacer layer includes: anonmagnetic metal layer including Ag, and at least one of a firstinsertion layer that is disposed on a bottom surface of the nonmagneticmetal layer and a second insertion layer that is disposed on a topsurface of the nonmagnetic metal layer, and wherein the first insertionlayer and the second insertion layer include an Fe alloy that isexpressed by General Formula (1):Fe_(γ)X_(1-γ)  (1), where X denotes one or more elements selected from agroup consisting of O, Al, Si, Ga, Mo, Ag, and Au, andγ satisfies 0<γ<1, wherein at least one of the first ferromagnetic layerand the second ferromagnetic layer includes a Heusler alloy that isexpressed by General formula (2):Co₂L_(α)M_(β)  (2), where L denotes one or more elements selected from agroup consisting of Mn and Fe, M denotes one or more elements selectedfrom a group consisting of Si, Al, Ga, and Ge,0.7≤α≤1.6, and0.65≤β≤1.35 wherein α and β in General formula (2) satisfy 2<α+β.
 2. Themagnetoresistive effect element according to claim 1, whereinγ in General Formula (1) satisfies 0.6≤γ≤0.9.
 3. The magnetoresistiveeffect element according to claim 2, wherein X in General formula (1) isone or more elements selected from a group consisting of Al, Si, and Ga.4. The magnetoresistive effect element according to claim 1, wherein αand β in General formula (2) satisfy:0.85≤α≤1.55, and0.75≈β≤1.25.
 5. The magnetoresistive effect element according to claim3, wherein α and β in General formula (2) satisfy:0.85≤α≤1.55, and0.75≤β≤1.25.
 6. The magnetoresistive effect element according to claim1, wherein 0.2 nm≤t1≤10 nm is satisfied where t1 denotes a thickness ofthe first insertion layer, and wherein 0.2 nm≤t2≤10 nm is satisfiedwhere t2 denotes a thickness of the second insertion layer.
 7. Themagnetoresistive effect element according to claim 1, wherein α and β inGeneral formula (2) further satisfyα+β2.75.
 8. A magnetic head comprising the magnetoresistive effectelement according to claim
 1. 9. A sensor comprising themagnetoresistive effect element according to claim
 1. 10. Ahigh-frequency filter comprising the magnetoresistive effect elementaccording to claim
 1. 11. An oscillator comprising the magnetoresistiveeffect element according to claim
 1. 12. The magnetoresistive effectelement according to claim 3, wherein 1≤α.
 13. The magnetoresistiveeffect element according to claim 12, wherein 0.2 nm≤t1≤10 nm issatisfied where t1 denotes a thickness of the first insertion layer, andwherein 0.2 nm≤t2≤10 nm is satisfied where t2 denotes a thickness of thesecond insertion layer.
 14. A magnetoresistive effect elementcomprising: a first ferromagnetic layer; a second ferromagnetic layer;and a spacer layer that is disposed between the first ferromagneticlayer and the second ferromagnetic layer, wherein the spacer layerincludes: a nonmagnetic metal layer, and at least one of a firstinsertion layer that is disposed on a bottom surface of the nonmagneticmetal layer and a second insertion layer that is disposed on a topsurface of the nonmagnetic metal layer, wherein the first insertionlayer and the second insertion layer include an Fe alloy that isexpressed by General Formula (1):Fe_(γ)X_(1-γ)  (1), where X denotes one or more elements selected from agroup consisting of Al, Ga and Ag, andγ satisfies 0.6≤γ≤0.9, wherein the first insertion layer is continuedfrom one side to the other side of the magnetoresistive effect elementin a transverse direction of the magnetoresistive effect element,wherein the second insertion layer is continued from one side to theother side of the magnetoresistive effect element in a transversedirection of the magnetoresistive effect element, wherein at least oneof the first ferromagnetic layer and the second ferromagnetic layerincludes a Heusler alloy that is expressed by General formula (2):Co₂L_(α)M_(β)  (2) where L denotes one or more elements selected from agroup consisting of Mn and Fe, M denotes one or more elements selectedfrom a group consisting of Si, Al, Ga, and Ge,1≤α,0.65≤β≤1.35, and2≤α+β.
 15. The magnetoresistive effect element according to claim 14,wherein 0.2 nm≤t1≤10 nm is satisfied where t1 denotes a thickness of thefirst insertion layer, and wherein 0.2 nm≤t2≤10 nm is satisfied where t2denotes a thickness of the second insertion layer.
 16. Themagnetoresistive effect element according to claim 14, wherein α and βin General formula (2) further satisfyα+β≤2.75.
 17. A magnetic head comprising the magnetoresistive effectelement according to claim
 14. 18. A sensor comprising themagnetoresistive effect element according to claim
 14. 19. Ahigh-frequency filter comprising the magnetoresistive effect elementaccording to claim
 14. 20. An oscillator comprising the magnetoresistiveeffect element according to claim
 14. 21. A magnetoresistive effectelement comprising: a first ferromagnetic layer; a second ferromagneticlayer; and a spacer layer that is disposed between the first:ferromagnetic layer and the second ferromagnetic layer, wherein thespacer layer includes: a nonmagnetic metal layer, and at least one of afirst insertion layer that is disposed on a bottom surface of thenonmagnetic metal layer and a second insertion layer that is disposed ona top surface of the nonmagnetic metal layer, and wherein the firstinsertion layer and the second insertion layer include an Fe alloy thatis expressed by General Formula (1):Fe_(γ)X_(1-γ)  (1), where X denotes one or more elements selected from agroup consisting of Mo and Au, andγ satisfies 0.6≤γ≤0.9, and wherein at least one of the firstferromagnetic layer and the second ferromagnetic layer includes aHeusler alloy that is expressed by General formula (2):Co₂LαMβ  (2), where L denotes one or more elements selected from a groupconsisting of Mn and Fe, M denotes one or more elements selected from agroup consisting of Si, Al, Ga, and Ge,0.7≤α≤1.6,0.65≤β≤1.35, and2<α+β.
 22. The magnetoresistive effect element according to claim 21,wherein 1≤α.
 23. The magnetoresistive effect element according to claim22, wherein 0.2 nm≤t1≤10 nm is satisfied where t1 denotes a thickness ofthe first insertion layer, and wherein 0.2 nm≤t2≤10 nm is satisfiedwhere t2 denotes a thickness of the second insertion layer.
 24. Themagnetoresistive effect element according to claim 21, wherein α and βin General formula (2) further satisfyα+β≤2.75.
 25. A magnetic head comprising the magnetoresistive effectelement according to claim
 21. 26. A sensor comprising themagnetoresistive effect element according to claim
 21. 27. Ahigh-frequency filter comprising the magnetoresistive effect elementaccording to claim
 21. 28. An oscillator comprising the magnetoresistiveof according to claim 21.